Case 20- Anatomy Flashcards
Blood flow in the brain- Myogenic autoregulation
When the pressure increases vasoconstriction occurs reducing cerebral blood flow. When the pressure decreases there is vasodilation. Autoregulation allows the maintenance of blood flow to the entire brain. Locally in specific regions of the brain CO2 and hydrogen ions cause vasodilationt
Outside the CPP autoregularity limit
- Cerebral blood flow becomes dependent on the mean arterial pressure in a linear fashion
- When the vessels are maximally dilated, they cannot compensate anymore and flow decreases as pressure decreases
- When the vessels are maximally constricted, they cannot compensate anyome and flow increases as pressure increases
Directions in the brain
When describing the brain, Rostral is forward towards the mouth and caudal is towards the back. Dorsal is up near the hair and ventral is down near the neck
Anatomy of the brainstem
Midbrain -> pons -> medulla oblongata
• Hindbrain- pons, medulla and cerebellum
• Bulb- pons and medulla
• Function= conduit and connections between the cerebrum and spinal cord
• Reticular formation- consciousness, respiration and CVS
• Cranial nerves III-XII nuclei
The Cerebral peduncle
The Cerebral peduncle connects the midbrain to the thalamus, it contains the: Crus cerebri (anterior), substantia nigra and the Tegmentum. The crus cerebri consists of axons of the Corticospinal, Corticobulbar and Corticopontine tracts. The space between the two cerebral peduncles is the interpeduncle fossa. The cerebellar peduncles are on the ventral surface
Midbrain dorsal surface
- Superior colliculus- eye movement and reflexes
* Inferior colliculus- auditory reflexes
Midbrain lateral view
- Tegmentum- contains the cranial nerve nuclei
- Tectum- superior and inferior colliculi
- Tegmentum is separated from the Tectum by the cerebral aqueduct which joins the third and fourth ventricle
Rostral level of the midbrain
- Superior colliculus (SC)
- Spinal lemniscus/medial lemniscus (SL/ML)
- Red nucleus (RN)
- Substantia nigra (SN)
- Crus cerebri (CC)- contains the descending motor nerves
Brainstem causal, level of inferior colliculus
- Inferior colliculus (IC)
- Decussation of superior cerebellar peduncle (DCP)
- Spinal lemniscus/medial lemniscus (SL/ML)
- Corticobulbar/corticospinal tracts (CB/CS)
Pons ventral surface
- Middle cerebellar peduncle- area of attachment between the pons and cerebelum
- Pontine swelling due to the transverse fibres between the pons and cerebellum
Pons dorsal surface
- Superior cerebellar peduncle
- Middle cerebellar peduncle
- The cerebellar peduncles form connection with the cerebellum
- Rhomboid fossa- forms the floor of the 4th ventricle
- Lateral aperture- allows the CSF to enter the subarachnoid space from the 4th ventricle
Mid-pons
- Trigeminal nerve (CN V)
- Corticospinal fibres (CS)
- Medial lemniscus (ML)
- Middle cerebellar peduncle (MCP)
- 4th ventricle- opens from the cerebral aqueduct
Medulla ventral surface
- Olives- contains the inferior olivary nucleus, forms connections with the cerebellum
- Pyramids- white matter containing the corticospinal tracts. Contain descending fibres from the motor cortex which pass through the internal capsule and are going to the spinal cord
Medulla- dorsal surface
- Inferior cerebellar peduncle
- Cuneate and gracile tubercle- formed by the dorsal column and carry information about fine touch and proprioception. The cuneate tubercle carry’s information from the upper limb and neck and the gracile tubercle carry’s information from the lower limbs and trunk
- Obex- CSF can enter the central canal of the spinal cord through this
- Fourth ventricle (floor)
Cranial nerves
There are 12 pairs of cranial nerves. They form part of the peripheral nervous system, the cranial nerves arise directly from the brain and brainstem.
The types of cranial nerves
- CN I Olfactory- Sensory
- CN II- Optic- Sensory
- CN III- Oculomotor- Motor
- CN IV- Trochlear- Motor
- CN V- Trigeminal- Both
- CN VI- Abducens- Motor
- CN VII- Facial- Both
- CN VIII- Vestibulocochlear- Sensory
- CN IX- Glossopharyngeal- Both
- CN X- Vagus- Both
- CN XI- Accessory (spinal)- Motor
- CN XII- Hypoglossal- Motor
Cranial nerve mnemonic
Cranial nerve mnemonic= Ooh, ooh, ooh, to touch and feel very good velvet. Such heaven!
Fibre type mnemomic- Some say my mother bought my brother some bad beer, my, my
Sensory function of cranial nerves
- GSA-General somatic afferent-General sensory function- pain, touch and temperature. Of the skin, bone and meninges includes oral cavity, nasal cavity and eye socket
- SSA-Special somatic afferent- sensation developing in the ectoderm e.g. sight, hearing, equilibrium or Special Visceral Afferent- special senses in conjunction with GIT e.g. taste, smell. These are special senses
Motor function of the cranial nerves
- General Somatic Efferent-to skeletal muscles. Muscles of eye and tongue movement (as well as shoulder)
- Special Visceral Efferent-Special motor to skeletal muscles that develop in the pharyngeal branchial arches-give rise to structures in the head and neck. The Branchial muscle such as muscles of mastication, swallowing, speech and facial expression
Autonomic function of the cranial nerves
- General Visceral Efferent- Motor to heart, smooth muscle and glands. These are part of the parasympathetic functions. Salivary glands, lacrimal glands, light reflexes, carotid body, thorax/abdo
- General Visceral Afferent- sensory from organs-smooth muscle, baroreceptor, chemoreceptors, glands e.g. heart and GIT.
Origin of cranial neves
• Cerebrum- cranial nerves 1 and 2 (olfactory and optic)
• Midbrain- cranial nerves 3 and 4
• Pons- cranial nerves 5 to 8
• Medulla- cranial nerves 9 to 12
In general the cranial nerves emerge from the ventral aspect, CNIV trochlear is an exception. In general the cranial nerves emerge sequentially from CN1-12, CN12 hypoglossal is the exception to this rule and is before CN XI. The motor nerve nucleus is more near the midline